Expressed sequence tags (ESTs) of follicle/interstitial cell enriched ovarian tissue from previtellogenic coho salmon

Little is known about previtellogenic oocyte growth in fish despite its importance in determining age of puberty. This study aimed to reveal ovarian genes expressed during previtellogenic growth in coho salmon (Oncorhynchus kisutch), a semelparous teleost that exhibits synchronous follicle development. Cortical alveolus stage ovaries were enriched for follicle/interstitial cell layers prior to RNA isolation to increase their contribution relative to abundant oocyte transcripts. A cDNA library was constructed and 1783 ESTs were analyzed. Numerous follicle/interstitial cell related genes were identified, including anti-Müllerian hormone, lipoprotein lipase, gonadal-soma derived growth factor, connective tissue growth factor, relaxin-3, basigin, and 3β-HSD. Claudin genes that may relate to cell-cell contact were also observed. Several genes involved in the regulation of apoptosis/atresia were identified, such as caspase-1, TNF receptor, and clusterin. Oocyte related genes identified included zona pellucida proteins, lectins, and cathepsins. This research sheds light on ovarian genes expressed during previtellogenic growth and provides tools for future candidate gene studies.